I find that amusing, but it's also true that the genetic risk from first cousins mating is believed to be really quite low. There doesn't seem to be any compelling evidence that states should be prohibiting that, either.

On the other hand, I've seen several same-sex-marriage opponents list "cousins getting married" as part of the slippery slope that letting MOTSSs get married will set off, so it's relevant to point out that it's already more legal.